fix: update logo reference from JPG to PNG

JPEG does not support transparency, causing colored corners
on dark backgrounds. The repo logo was converted to PNG in
attune-io/attune#43.

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>

Author: SebTardif

profile/README.md

@@ -1,5 +1,5 @@
 <p align="center">
-  <img src="https://raw.githubusercontent.com/attune-io/attune/main/docs/logo.jpg" alt="Attune" width="120">
+  <img src="https://raw.githubusercontent.com/attune-io/attune/main/docs/logo.png" alt="Attune" width="120">
 </p>
 
 <h3 align="center">Safe, in-place Kubernetes pod resource right-sizing</h3>